This invention relates to local area networks and, more particularly, to an arrangement whereby a broadcast oriented system can be used in conjunction with a connection oriented system.
In communication systems there are basically two types of systems, namely, connectionless and connection oriented. Connectionless systems are broadcast oriented such that every end-system monitors all transmissions and responds when it "hears" its own address. In a connection oriented system a calling end-system calls (using some code) a called end-system and the network acts to establish a communication linkage between the calling and called system. The typical telecommunication system (when the end-systems are telephones) operates in the connection oriented mode.
One use of connectionless (broadcast) systems is for establishing Local Area Networks (LANs) where a number of end-systems, such as host computers and personal computers (PCs), can become "connected" for the interchange of data. However, since connectionless LANs are inherently limited in size, confined to a local area, and difficult to move or re-configure due to the nature of the broadcast media, it is often desired to take the features of a connectionless LAN and emulate then with a connection oriented network. However, the services and features provided by a typical connectionless LAN, e.g., datagram services and name services, rely on the broadcast nature of the network where every end-system monitors all transmissions. Thus, these services do not inherently work in a connection oriented network because in such networks communications are only directed to particular end-systems and are not broadcasted to all end-systems.
A problem in a connectionless LAN is that, while any end-system on the LAN can communicate with any other end-system on the LAN, they do so with no security control. Thus, it is a desirable feature to add security to a connectionless network such that calls between end-systems are authorized before completion.
A further problem with connectionless LANs is their limited bandwidth since in such systems every transmission is monitored, thereby requiring every end-system active on the LAN to process large amounts of otherwise useless data in order to determine which transmissions are destined for it.
One solution to these problems has been to provide a centralized process within connection oriented system that acts as a server to each end-system. Each end-system is then connected to the server via a special connection, referred to as an umbilical connection, over which the end-system and the server communicate with one another. The server relies upon both administered information (information stored in the server) and information that is dynamically on a connection-by-connection basis obtained from each end-system in order to accept data transmission from the end-systems over the umbilical connections. When appropriate, the server directs data transmissions to specified destination end-systems over the umbilical connections. Based on dialogues carried out over these umbilical connections, the server also mediates the establishment of direct connections between end-systems. Thus, it is the server that controls the communication between all end-systems.
This, however, only solves part of the problem. There remains the problem that the server does not know the identity of the end-systems.